Helianthus silphioides
Ozark sunflower, rosinweed sunflower
erect, hispid to strigoso-hispid proximally, glabrate distally.
basal and cauline; mostly opposite;
petioles 0.1–5.5 cm;
blades ovate to broadly ovate or suborbiculate, 7–15 × 4.5–15 cm, bases rounded to truncate or ± cuneate, margins entire or crenate to serrate, abaxial faces usually scabrous, sometimes ± strigose (hairs on midribs to 1 mm), not gland-dotted (cauline 9+ pairs proximal to heads, smaller).
0.5–10 cm.
hemispheric, 10–20 mm diam.
8–13;
laminae 15–20 mm (abaxial faces not gland-dotted).
75+;
corollas 6–7 mm, lobes reddish;
anthers dark, appendages dark (style branches yellow).
16–23, oblong to obovate, 8–10 × 3–5 mm, (margins ciliolate) apices obtuse to acute, sometimes mucronate, abaxial faces glabrous or glabrate.
3–15+.
3–4 mm, glabrous or distally puberulent;
pappi of 2 aristate scales 2.5–2.7 mm.
9–10 mm, entire or ± 3-toothed.
= 34.
Helianthus silphioides
Similar to Helianthus atrorubens, H. silphioides is distinguished by shorter hairs (less than 2 mm) on stems proximally and on abaxial leaf midveins, and by petioles of basal leaves less than 1/2 lengths of blades and winged less than 1/2 their lengths. As befits the name, specimens of H. silphioides (and also H. atrorubens) are not infrequently misidentified as species of Silphium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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